Optical distance measuring device may utilize 3D image sensing system to collect the distance/depth information related to a target. Through the distances/depths corresponding to the pixels of the 3D images, 3D image data is formed. 3D images are also called as distance images or depth images. The extra distance dimension may be applied in various applications, so as to obtain information between the camera and the object, to accomplish different tasks in the sensing area in the field.
In general, 3D image sensing system emits incident light by light emitting diode (LED), and utilizes pixel circuits in a pixel array to receive a reflected light corresponding to the incident light. However, in the prior art, the pixel circuit applied in the 3D image sensing system in the art needs to operate in a condition that manufacturing of the semiconductor devices and the clock signals are perfectly matched up, so as to determine the depth information correctly. In reality, manufacturing of the semiconductor devices and the clock signals are usually not matched, causing that the image sensing system is not able to obtain the depth information accurately. In addition, when the pixel circuit senses the reflected light, it would be affected by the ambient light, which would cause the common mode voltage of the output signal of the pixel circuit being too large, occupy too much dynamic range of the backend amplifier, and cause the backend amplifier entering into a saturation status easily.
Therefore, it is necessary to improve the prior art.